Edwin Powell Hubble (November 20, 1889 – September 28, 1953)[1] was an American astronomer who played a crucial role in establishing the field of extragalactic astronomy and is generally regarded as one of the most important observational cosmologists of the 20th century. Hubble is known for showing that the recessional velocity of a galaxy increases with its distance from the earth, implying the universe is expanding,[2] known as "Hubble's law", although a preliminary version of this relation was proposed by Georges Lemaître two years earlier in a less prominent journal.

Edwin Hubble is also known for providing substantial evidence that many objects then classified as "nebulae" were actually galaxies beyond the Milky Way.[3] A decade before, the American astronomer Vesto Slipher had provided the first evidence that the light from many of these nebulae was strongly red-shifted, indicative of high recession velocities.[4][5] Hubble's name is most widely recognized for the Hubble Space Telescope which was named in his honor, with a model prominently displayed in his hometown of Marshfield, Missouri.

Edwin Hubble was born to Virginia Lee Hubble (née James) (1864–1934)[6] and John Powell Hubble, an insurance executive, in Marshfield, Missouri, and moved to Wheaton, Illinois, in 1900.[7] In his younger days, he was noted more for his athletic prowess than his intellectual abilities, although he did earn good grades in every subject except for spelling. Edwin was a gifted athlete playing baseball, football, basketball, and he ran track in both high school and college. He played a variety of positions on the basketball court from center to shooting guard. In fact Hubble even led the University of Chicago's basketball team to their first conference title in 1907.[8] He won seven first places and a third place in a single high school track and field meet in 1906.

In 1909, Hubble's father moved his family from Chicago to Shelbyville, Kentucky, so that the family could live in a small town, ultimately settling in nearby Louisville. His father died in the winter of 1913, while Edwin was still in England, and in the summer of 1913, Edwin returned to care for his mother, two sisters, and younger brother, as did his brother William. The family moved once more to Everett Avenue, in Louisville's Highlands neighborhood, to accommodate Edwin and William.[11]

Hubble was also a dutiful son, who despite his intense interest in astronomy since boyhood, surrendered to his father's request to study law, first at the University of Chicago and later at Oxford, though he managed to take a few math and science courses. After the death of his father in 1913, Edwin returned to the Midwest from Oxford, but did not have the motivation to practice law. Instead, he proceeded to teach Spanish, physics and mathematics at New Albany High School in New Albany, Indiana, where he also coached the boys' basketball team. After a year of high-school teaching, he entered graduate school with the help of his former professor from the University of Chicago to study astronomy at the university's Yerkes Observatory, where he received his PhD in 1917. His dissertation was titled "Photographic Investigations of Faint Nebulae".[12]

After the United States declared war on Germany in 1917, Hubble rushed to complete his PhD dissertation so he could join the military. Hubble volunteered for the United States Army and was assigned to the newly created 86th Division. He rose to the rank of lieutenant colonel,[13] and was found fit for overseas duty on July 9, 1918, but the 86th Division never saw combat. After the end of World War I, Hubble spent a year in Cambridge, where he renewed his studies of Astronomy.[14] In 1919, Hubble was offered a staff position at the Carnegie Institution's Mount Wilson Observatory, near Pasadena, California, by George Ellery Hale, the founder and director of the observatory. Hubble remained on staff at Mount Wilson until his death in 1953. Shortly before his death, Hubble became the first astronomer to use the newly completed giant 200-inch (5.1 m) reflector Hale Telescope at the Palomar Observatory near San Diego, California.

Hubble also worked as a civilian for U.S. Army at Aberdeen Proving Ground in Maryland during World War II as the Chief of the External Ballistics Branch of the Ballistics Research Laboratory during which he directed a large volume of research in exterior ballistics which increased the effective fire power of bombs and projectiles. His work was facilitated by his personal development of several items of equipment for the instrumentation used in exterior ballistics, the most outstanding development being the high-speed clock camera, which made possible the study of the characteristics of bombs and low velocity projectiles in flight. The results of his studies were credited with greatly improving design, performance, and military effectiveness of bombs and rockets. For his work there, he received the Legion of Merit award.[15]

Hubble had a heart attack in July 1949 while on vacation in Colorado. He was taken care of by his wife, Grace Hubble, and continued on a modified diet and work schedule. He died of cerebral thrombosis (a spontaneous blood clot in his brain) on September 28, 1953, in San Marino, California. No funeral was held for him, and his wife never revealed his burial site.[18][19][20]

Edwin Hubble's arrival at Mount Wilson Observatory, California in 1919 coincided roughly with the completion of the 100-inch (2.5 m) Hooker Telescope, then the world's largest. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope at Mt. Wilson, Hubble identified Cepheid variables (a kind of star that is used as a means to determine the distance from the galaxy[21][22] – see also standard candle) in several spiral nebulae, including the Andromeda Nebula and Triangulum. His observations, made in 1922–1923, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own, suspected by researchers at least as early as 1755 when Immanuel Kant's General History of Nature and Theory of the Heavens appeared. This idea had been opposed by many in the astronomy establishment of the time, in particular by the Harvard University-based Harlow Shapley. Despite the opposition, Hubble, then a thirty-five-year-old scientist, had his findings first published in The New York Times on November 23, 1924,[23] and then more formally presented in the form of a paper at the January 1, 1925 meeting of the American Astronomical Society.[24]

Hubble's findings fundamentally changed the scientific view of the universe. Supporters state that Hubble's discovery of nebulae outside of our galaxy helped pave the way for future astronomers.[25] Although some of his more renowned colleagues simply scoffed at his results, Hubble ended up publishing his findings on nebulae. This published work earned him an award titled the American Association Prize and five hundred dollars from Burton E. Livingston of the Committee on Awards.[8]

In 1929, Hubble examined the relation between distance and redshift of galaxies. Combining his measurements of galaxy distances with measurements of the redshifts of the galaxies by Vesto Slipher, and by his assistant Milton L. Humason, he found a roughly linear relation between the distances of the galaxies and their redshifts,[2] a discovery that later became known as Hubble's law.

Yet the reason for the redshift remained unclear. It was Georges Lemaître, a Belgian Catholic priest and physicist, who found that Hubble's observations supported the Friedmann model of an expanding universe based on Einstein's equations for General Relativity, which is now known as the Big Bang theory. This meant, the greater the distance between any two galaxies, the greater their relative speed of separation. If interpreted that way, Hubble's measurements on 46 galaxies lead to a value for the Hubble Constant of 500 km/s/Mpc, which is much higher than the currently accepted value due to errors in their distance calibrations.

Hubble himself remained doubtful about Lemaître's interpretation. In 1931 he wrote a letter to the Dutch cosmologist Willem de Sitter expressing his opinion on the theoretical interpretation of the redshift-distance relation:[27]

Mr. Humason and I are both deeply sensible of your gracious appreciation of the papers on velocities and distances of nebulae. We use the term 'apparent' velocities to emphasize the empirical features of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority.

Today, the "apparent velocities" in question are understood as an increase in proper distance that occurs due to the expansion of space. Light traveling through stretching space will experience a Hubble-type redshift, a mechanism different from the Doppler effect (although the two mechanisms become equivalent descriptions related by a coordinate transformation for nearby galaxies).

In the 1930s, Hubble was involved in determining the distribution of galaxies and spatial curvature. These data seemed to indicate that the universe was flat and homogeneous, but there was a deviation from flatness at large redshifts. According to Allan Sandage,

Hubble believed that his count data gave a more reasonable result concerning spatial curvature if the redshift correction was made assuming no recession. To the very end of his writings he maintained this position, favouring (or at the very least keeping open) the model where no true expansion exists, and therefore that the redshift "represents a hitherto unrecognized principle of nature."[28]

There were methodological problems with Hubble's survey technique that showed a deviation from flatness at large redshifts. In particular, the technique did not account for changes in luminosity of galaxies due to galaxy evolution. Earlier, in 1917, Albert Einstein had found that his newly developed theory of general relativity indicated that the universe must be either expanding or contracting. Unable to believe what his own equations were telling him, Einstein introduced a cosmological constant (a "fudge factor") to the equations to avoid this "problem". When Einstein learned of Hubble's redshifts, he immediately realized that the expansion predicted by General Relativity must be real, and in later life he said that changing his equations was "the biggest blunder of [his] life." In fact, Einstein apparently once visited Hubble and tried to convince him that the universe was expanding.[29] Hubble also discovered the asteroid1373 Cincinnati on August 30, 1935. He wrote The Observational Approach to Cosmology and The Realm of the Nebulae approximately during this time.

At the time, the Nobel Prize in Physics did not recognize work done in astronomy. Hubble spent much of the later part of his career attempting to have astronomy considered an area of physics, instead of being its own science. He did this largely so that astronomers—including himself—could be recognized by the Nobel Prize Committee for their valuable contributions to astrophysics. This campaign was unsuccessful in Hubble's lifetime, but shortly after his death, the Nobel Prize Committee decided that astronomical work would be eligible for the physics prize.[8] However, the prize is not one that can be awarded posthumously.

Often called a "pioneer of the distant stars," astronomer Edwin Hubble (1889–1953) played a pivotal role in deciphering the vast and complex nature of the universe. His meticulous studies of spiral nebulae proved the existence of galaxies other than our own Milky Way. Had he not died suddenly in 1953, Hubble would have won that year's Nobel Prize in Physics.

^ abcGale E. Christianson (1996). Edwin Hubble: mariner of the nebulae. University of Chicago Press. p. 362. Grace heard that Enrico Fermi and Subrahmanyan Chandrasekhar, both members of the Nobel Committee, had joined their colleagues in unanimously voting Hubble the prize in physics, a rumor later confirmed by the astronomers Geoffrey and Margaret Burbidge after speaking with "Chandra".

^Gale E. Christianson (1996). Edwin Hubble: Mariner of the Nebulae. University of Chicago Press. p. 183. ISBN9780226105215. One morning, while driving north with Grace after the failed eclipse expedition of 1923, he broached Whitehead's idea of a God who might have chosen from a great many possibilities to make a different universe, but He made this one. By contemplating the universe, one might approximate some idea of its Creator. As time passed, however, he seemed even less certain: "We do not know why we are born into the world, but we can try to find out what sort of a world it is — at least in its physical aspects." His life was dedicated to science and the objective world of phenomena. The world of pure values is one which science cannot enter, and science is unconcerned with the transcendent, however compelling a private revelation or individual moment of ecstasy. He pulled no punches when a deeply depressed friend asked him about his belief: "The whole thing is so much bigger than I am, and I can't understand it, so I just trust myself to it; and forget about it."

^Tom Bezzi (2000). Hubble Time. iUniverse. p. 93. ISBN9780595142477. John terribly depressed, and asked Edwin about his belief. Edwin said, "The whole thing is so much bigger than I am, and I can't understand it, so I just trust myself to it, and forget about it." It was not his nature to speculate. Theories, in his opinion, were appropriate cocktail conversation. He was essentially an observer, and as he said in The Realm of the Nebulae: "Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation." Edwin never exhausted those empirical resources. "I am an observer, not a theoretical man," he attested, and a lightly spoken word in a lecture or in a letter showed that observation was his choice.